Although alcohol has been in use for thousands of years, studies of its effect on the human body, mind and behaviour do not have such a long tradition. This is even more true when it comes to the impact it has on our behaviour when we are flying on commercial aircraft – at altitude, albeit in pressurised cabins. Marija Zuzek PhD ponders the question as to whether one drink on the ground is really the same as two in the skies.
Alcohol is a low-density liquid which, in its purest form, is devoid of colour or smell. Alcohol is produced through fermentation, the process of converting of sugar to alcohol, then distillation to increase the alcohol by volume (ABV) and results in the alcohol that is used for consumption (ethyl alcohol).
There is no precise evidence as to how and when people first learned to control the process of fermentation but historical findings indicate that alcohol may have been consumed as early as 9000 B.C. with clear evidence that it was consumed as early as 5000 B.C. in ancient Babylon, whose inhabitants drank a type of beer as part of a religious ritual, and around 3000 B.C. in Mesopotamia where wine was consumed.
Over the centuries, wine and beer were primarily subjected to a process of natural fermentation which resulted in relatively low alcohol content, 5-8% ABV in beer and approximately 12% ABV in wine. The reason for this is that yeast, acting as a catalyst in the fermentation process, is not resistant to, and cannot ‘survive’, an alcohol concentration level higher than 14%. Subsequent fermentation control methods and the development of the distillation process created the conditions to produce alcohol distillates with higher alcohol content. The process of distillation is thought first to have been discovered in Arabia in the 8th century and then rediscovered five centuries later by a university professor of medicine in France. During distillation, the fermented beverage is heated to evaporation point and then cooled in order to produce condensation and a distillate with significantly higher alcohol content.1
The Effect of Alcohol on the Human Body and Behaviour
Notwithstanding the fact that alcohol has its benefits in medicine and pharmacology – or can be used as fuel, alcohol or ethanol (C2H5OH) – in the form of a beverage it is a psychoactive and neurotoxic2 substance and, as such, is one of the oldest recreational drugs. Despite the widespread belief that consuming alcohol stimulates an individual’s mood and activity, alcohol acts as an inhibitor on the brain and its effect is retrograde. In fact, alcohol accelerates the heart rate, increases blood flow, and stimulates brain cells to speed the transmission of nerve impulses. As a result, in its first stage, inebriation creates the illusion of boosting activity and mood, while actually slowing down reflexes due to its effect on the central nervous system (brain and spinal cord). In that condition, the individual, depending on the level of intoxication, shows a lack of physical coordination, concentration and may have difficulty speaking. Additionally, the extent of an individual’s inebriation inevitably leads to a change in their behaviour – a so-called ‘emotional release’ – and/or an apparent diminishing of fear and anxiety.
“…in the form of a beverage it is a psychoactive and neurotoxic substance and, as such, is one of the oldest recreational drugs…”
During consumption, approximately 20% of the alcohol enters the bloodstream through the stomach while the rest is absorbed into the bloodstream through the small intestines with the blood vessels speeding up the absorption. The fact that the brain is a ‘fatty’ organ and that the heart pumps significant amounts of blood to it means that the effect of alcohol on the consumer’s brain is instantaneous. The central nervous system, which otherwise controls voluntary and involuntary physical actions (such as respiration or heart action) branches out throughout the entire body and, accordingly, alcohol slows down the signals the brain ‘emits’ to the body, i.e. to the cells through neurotransmitters.3
The brain communicates through neurons, nerve cells that are specialized to receive and rapidly conduct chemical and electrical signals. Electrical signals help fulfil the neuron’s major role – to communicate information quickly to the rest of the body so that the brain can carry out its many functions. Neurotransmitters in each cell enable these signals to travel from the brain to all parts of the body. The Tenth Special Report states, “Alcohol appears to affect the function of several neurotransmitters by altering the communication mechanism between neurons. A large body of evidence suggests that this effect of alcohol on transmission [of signals from the brain] is the major change in the brain that gives rise to intoxication.” In simple terms, this means that alcohol works on the cellular level to disrupt communication from the brain, resulting in the physical, mental, and emotional behaviours associated with intoxication.
Source: Tenth Special Report to the U.S. Congress on Alcohol and Health, Uschan V. Michael, Alcohol, San Diego: CA, Lucent Books, 2002, pg. 32
As a result, intoxication does not occur after one, but rather after several alcoholic drinks because there must be a higher alcohol content in the bloodstream before it will start affecting the brain. The level of intoxication or inebriation is individual and depends on a variety of factors but mainly on the speed with which the liver is able to ‘process’ the quantity of alcohol consumed. The healthy liver of a middle-aged person has the ability to eliminate 0.5 ounces (0.015 litres) of pure alcohol from the bloodstream each hour, which is the equivalent of 12 ounces of beer (0.35 litres), 5 ounces of table wine (0.15 litres), or 1.5 ounces of 80-proof distilled spirits (0.04 litres).4
The amount of alcohol in a person’s bloodstream is referred to as blood alcohol level (BAL) or blood alcohol concentration (BAC). It is recorded in milligrams of alcohol per 100 millilitres of blood; a BAC of 0.10 means that 1/10 of 1 percent of total blood content is alcohol. A reading of 0.10 percent is considered legal proof that a person is drunk in most states. Figures are rounded to nearest .01. BACs shown are approximate, since they can be affected by factors other than weight.
Blood Alcohol Concentration Within One Hour
At 0.03 to 0.05 percent, a flushed face, feeling of euphoria, and increased social confidence; at 0.50 to 0.15 percent, disturbed thinking and coordination, reduced self-control, irresponsible talk and behaviour; at 0.15 to 0.25 percent, confused thinking, unsteady gait, slurred speech; at 0.25 to 0.40 percent, extreme confusion and disorientation, difficulty remaining upright, drowsiness, risk of falling into a coma (a state of deep unconsciousness from which the person cannot be aroused); 0.40 to 0.50 percent, risk of death due to cessation of breathing (although habitual drinkers may survive even such high levels).
Source: Uschan V. Michael, Alcohol, San Diego:CA, Lucent Books, 2002, pg. 29
While the body processes the alcohol through a series of chemical reactions, with the liver playing the most important role, the consumption of quantities of alcohol greater than those mentioned above in an hour will lead to greater alcohol content in the bloodstream and thereby to greater intoxication. Continuing to consume alcohol will slow down the nerves and brain activity and will result in a depressed effect. Similarly to its effect on the physical behaviour of the person drinking, alcohol will also have a direct impact on their ability to concentrate, reason, think, speak, and recall. In these circumstances and given the momentary ‘malfunctioning’ of the brain, extreme changes of mood often occur, ranging from sorrow to aggression, and the release of emotions. People who are drunk have trouble controlling emotions such as anger, causing some drinkers to behave violently. However, the degree of intoxication from drinking the same amount of alcohol will vary among individuals and even in the same individual on different occasions. This is because several important factors influence how rapidly alcohol will make someone intoxicated.5
“…extreme changes of mood often occur, ranging from sorrow to aggression, and the release of emotions…”
The way in which alcohol will affect the system of the person drinking will largely depend on their general health and weight, which will play an extremely important part in determining the effect intoxication will have in any given case, even in the same person. In other words, the same amount of alcohol will have a dramatically different effect on someone who weighs 230 pounds (104.3 kg) than on someone who weighs just 130 pounds (59 kg). Because the blood supply is correspondingly bigger, a similar amount of alcohol will be more diluted in the larger person’s body. Another important factor is the amount of time that has elapsed since the person drinking had their last meal, because food slows down the absorption of alcohol in the bloodstream. There are also individual variances in the speed with which people metabolise alcohol because of their own unique body chemistry. The sex of the drinker makes a difference because women usually absorb and metabolise alcohol more quickly than men, which means they will have higher BACs after consuming the same amount of alcohol. A final key factor is whether the person having a drink is a regular drinker as the bodies of those who drink frequently build up a tolerance to alcohol which slows down its effects.6
Alcohol in Cabin Air Pressure Conditions7
In order to understand the effect altitude and pressure have on the human body, we must first understand what happens to the air at high altitude. At sea level the particles in the air are more tightly compressed, meaning that oxygen is more concentrated. As you climb higher, however, the pressure decreases, air particles become more scattered and oxygen becomes less concentrated. This means that, if you were to take a deep breath at high altitude your body would take in less oxygen than it would at sea level. To give you an idea, at sea level the air pressure is around 101.3kPa (kilopascals). Whereas, at 16,000ft, the pressure drops to approximately 54.8kPa, and at 29,000ft it drops further to approximately 31kPa, less than a third of the air pressure at sea level.
By reducing air pressure, the exchange between ambient gases and the human body is also reduced, leading to a reduction in the absorption of oxygen8 through the lungs. When the body suddenly gets less oxygen, it tries to compensate and uses other means to take in more. As a result, your breathing will become faster, both your heart rate and metabolism will increase, and you may urinate more often which can also result in dehydration.
In normal conditions on passenger aircraft, cabin pressure is artificially maintained at a level equivalent to the outside air pressure at 6,000-8,000ft. Pressure is, therefore, not equal to that at sea level. In these conditions of reduced pressure, the body’s absorption of oxygen is also reduced.9 Bearing in mind that around 60% of the world’s population lives 1,000ft or less above sea level, if a person drinks alcohol in these conditions, or if a person who is already under the influence of alcohol boards a plane, their body will have a lower level of resistance to alcohol than in more oxygen rich conditions and, as such, their cognitive as well as motor abilities will be weaker.
Likewise, a healthy person’s blood pressure in resting conditions on the ground are likely to be roughly 120/80, and their pulse will be around 70-80. Alcohol consumption in these conditions will inevitably lead to heightened blood pressure (systolic and diastolic) and a quickening pulse. These reactions of the body to alcohol in cabin conditions will be more pronounced due to lower air pressure. The effect of alcohol on the same person’s body will differ considerably during consumption of the same amount of alcohol on the ground and in the air.
It is safe to say that the effect of alcohol on the human body and behaviour in cabin conditions is undoubtedly variable and subject to fluctuations depending on a number of factors: body weight, mental health, momentary mental state and stability, any medical conditions or acute disorders, cardio-vascular conditions, age, the quantity of consumed alcohol, etc. In these circumstances it is impossible to predict whether a person who is under the influence of alcohol will become aggressive towards other passengers in the restricted space of the passenger cabin on-board an airplane.10
“…if a person who is already under the influence of alcohol boards a plane, their body will have a lower level of resistance to alcohol than in conditions of a ‘richer’ mixture of gases and higher atmospheric pressure on the ground. In other words, their cognitive as well as motor abilities will be weaker…”
Since it has been proven that alcohol consumption can lead to numerous reactions on the part of the person who drank, ranging from exhilaration to aggressiveness, the limited space of the passenger cabin and easy access to safety handles for emergency door exit – requires every risk, including this one – to be reduced to a minimum.
Marija Zuzek PhD is an advisor within the Ministry of Defence of the Republic of Serbia. Holding a doctorate in the field of political sciences, since 2005 she has been actively involved in numerous international scientific conferences and round tables as an expert lecturer. Her professional experience also includes a diplomatic engagement. She can be contacted at: firstname.lastname@example.org
- Uschan V. Michael, Alcohol, San Diego:CA, Lucent Books, 2002, pg. 9-11; Fleming Alice, Alcohol: The Delightful Poison, New York: Delacorte, 1975, pg. 3
- ‘10th Special Report to the U.S. Congress on Alcohol and Health: Highlights from Current Research’, National Institute of Health, National Institute on Alcohol Abuse and Alcoholism, U. S. Department of Health and Human Services, 2000, pg. 134-146
- Uschan V. Michael, Alcohol, San Diego:CA, Lucent Books, 2002, pg. 23-26. See also: Dr David G. Newman, Alcohol and Human Performance from an Aviation Perspective: A Review, Australian Transport Safety Bureau, Research Report, 2004
- Katherine Ketcham Katherine, William F. Asbury, Beyond the Influence: Understanding and Defeating Alcoholism, New York: Bantam Books, 2000, pg. 30
- Uschan V. Michael, Alcohol, San Diego:CA, Lucent Books, 2002, pg. 28-33. See also: Dr David G. Newman, Alcohol and Human Performance from an Aviation Perspective: A Review, Australian Transport Safety Bureau, Research Report, 2004 and Jeffrey R. Davis, Robert Johnson, Jan Stepanek, Jennifer A. Fogarty, Fundamentals of Aerospace Medicine, Kluwer Wolters Wilkins & Williams Lippincott, Philadelphia, 2008
- Uschan V. Michael, Alcohol, San Diego:CA, Lucent Books, 2002, pg. 34-35 and Jeffrey R. Davis, Robert Johnson, Jan Stepanek, Jennifer A. Fogarty, Fundamentals of Aerospace Medicine, Kluwer Wolters Wilkins & Williams Lippincott, Philadelphia, 2008
- This part of the article was written with the expert support of the Military Test Pilot LtC Tomislav Becagovic, Flight Test Centre of the Serbian Armed Forces.
- Air is a combination of the following gases: nitrogen (N) 70%, oxygen (O2) 20%, and the remainder consists of hydrogen (H), other inert gases, carbon dioxide (CO2) and several trace gases.
- See also: Ernsting’s Aviation and Space Medicine, Edited by David P. Gradwell and David J. Rainford, CRC Press Taylor & Francis Group, LLC, Boca Raton FL, 2016
- See details of court trials due to alcohol consumption and/or presence of intoxicated passengers on board at: https://casetext.com/case/air-line-pilots-association-2
- 10th Special Report to the U.S. Congress on Alcohol and Health: Highlights from Current Research, National Institute of Health, National Institute on Alcohol Abuse and Alcoholism, U. S. Department of Health and Human Services, 2000
- Court trials: https://casetext.com/case/air-line-pilots-association-2
- Dr David G. Newman, Alcohol and Human Performance from an Aviation Perspective: A Review, Australian Transport Safety Bureau, Research Report, 2004
- Ernsting’s Aviation and Space Medicine, Edited by David P. Gradwell and David J. Rainford, CRC Press Taylor & Francis Group, LLC, Boca Raton FL, 2016
- Jeffrey R. Davis, Robert Johnson, Jan Stepanek, Jennifer A. Fogarty, Fundamentals of Aerospace Medicine, Kluwer Wolters Wilkins & Williams Lippincott, Philadelphia, 2008
- Katherine Ketcham Katherine, William F. Asbury, Beyond the Influence: Understanding and Defeating Alcoholism, New York: Bantam Books, 2000
- Uschan V. Michael, Alcohol, San Diego: CA, Lucent Books, 2002, pg. 9-11; Fleming Alice, Alcohol: The Delightful Poison, New York: Delacorte, 1975